If you put Quality In you get Quality Out

SOIL COMPACTION AFFECTS FERTILISER EFFCIENCY

Key to maximising returns from grassland next spring is caring for soil over the autumn. Independent consultant, Dr George Fisher, gives some timely advice for dairy farmers keen to reap the rewards of quality silage and grazing.

“It’s a reality that we’re seeing more soil compaction on grassland farms than ever… both from a growth in the use of heavy machinery, and from pressures on grazing with higher stock densities. With the milk price where it is, dairy farmers need to be looking for every opportunity to reduce costs, and getting more from home grown forage is one of the easiest routes for most to take,” he says.

A recent ADAS survey has shown that as much as 70% of the grassland soils in England and Wales show signs of compaction, and some of the latest AHDB Dairy research starts to put a cost on this, saying that yield losses of up to two tonnes/ha can be seen.

Coupled with poor nitrogen recovery, as up to 40% can be lost, and high water retention delaying spring turnout, compaction can cost in excess of £250/ha in lost sward productivity and utilisation, the AHDB Dairy findings report.

Increased use of contractors, who will often bring in bigger and heavier machinery to complete silage operations quickly, is believed to be one of the reasons behind this compaction issue.

“Farmers often don’t think about the amount of movement on their grassland, starting with slurry application, and following on with fertilising, mowing, forage harvesting, baling and the use of bigger tractors and trailers. When any of this farm work happens in slightly wet conditions, the effect is even more severe,” says George. Up to 80% of the field can be driven over, and the higher the clay content of the soil, the higher the compaction.

He warns dairy farmers to be particularly aware of these issues this autumn, saying that 2015 has been a fantastic year for grass growth, and while many second silage cuts are in the clamp, farmers are indicating they will go for the third cut this year as they bid to increase home grown forage use and reduce concentrate costs.

“Those taking a third cut must take even more care,” he says. “It’s true that 60% of the compaction comes from the first pass across the land, but the more traffic there is, the bigger the problem can become.”

He says the ideal balance allows for one third soil, one third air, and one third water. “Imagine the soil as a sponge, if compaction squeezes out all the air and water, when the rains come the water just runs off the top surface, it can’t be absorbed into the soil, and the problem increases as the ground can’t ‘wet up’ in the next spring. This, in turn, means the nitrogen applied is not getting down into the soil profile as it should do. Really compacted soil can hold seven times less water than a non-compacted soil.”

So how can you check the healthiness of your soil?

According to ADAS, SRUC and AHDB work, there are four easy steps to take:

A surface assessment where farmers look at sward quality to identify potentially damaged areas which will require further assessment. When the sward is ‘good’, it will be intact, with no poaching and few wheelings. Moderate will show a poached surface with some wheelings and more weed species. Poor will show the surface compacted, soil exposed, poaching and poor sward quality.

For moderate or poor areas, the next step is soil extraction and inspection, digging out one spade-sized block of soil to a depth of approx 30cm. Cut down on three sides, then lever the block out, leaving one side undisturbed.

Gently open the soil block like a book to break it up. If the structure is uniform, assess the block as a whole. If there are two or more horizontal layers of differing compacted structure, identify the layer with the poorest structure. Carry out the rest of the assessment on this limiting layer

Break up the soil with your hands into smaller units and assign a score based on what you see. A score of one or two is good, where the soil easily breaks apart in small clumps. A score of three is moderate and four or five is poor and requires management action, for these scores the soil will be more difficult to break apart and will remain in palm to hand sized compacted chunks.

A guide chart which uses photographs to indicate how to score is available from AHDB Dairy.

“Rejuvenating soil structure can lead to increases of 15% in grass yield,” says George. “Both sward lifting and spiking can help to alleviate the problem, but it’s important the right technique is used at the right time, otherwise you can make the problem worse rather than solving it.”

As well as losing yield and energy, George says it’s easy to see losses from farm fertiliser costs. “When you’re losing 40% of your fertiliser potential through compaction, and a good quality fertilier like Nitram® is costing around £240/tonne, you’re losing £96 for every tonne you apply,” he says. Taking an average application rate of 250kgs/ha, across 40ha, can mean you are ‘throwing away’ £3000 worth of quality product.

“No-one can afford to do that,” he says. “It’s really vital that soil health is made a priority on every grassland farm going forwards.”

As well as nutrient losses, there are yield losses to think about too. “Consider that instead of 10 tonnes/DM/ha you are only able to get 8 tonne/DM/ha from reduced fertiliser availability. A two-tonne drop, at 11MJ energy, is a loss of 22,000MJ – that’s enough energy for 4000 litres of milk. With an average milk price of 24p/litre, that’s a loss of £977.

“You also have to consider the cost of buying in energy to replace that loss – 1.6 tonnes of concentrates at £225/tonne – about £360 at today’s prices.”

Regardless of your grazing system, George is adamant that there are ways to move forward and save costs. “My message to all dairy farmers would be to take time this autumn to ensure your swards are in tip top condition for next spring. Grass continues to be the most cost-efficient feed on your farm, and it makes absolute sense to spend time ensuring it can perform at its best.”